1. Field of the Invention
This invention relates to an improvement in an injection device for a dental anesthetic or the like utilized when a dentist injects an anesthetic into a patient's gingiva for the dental treatment of a patient in dental care.
2. Description of the Prior Art
A means disclosed in Japanese Utility Model Laid-open No. 53-43748 has been known with reference to an injection device for a dental anesthetic or the like.
With respect to this means, a main body a is formed by mounting integrally and continuously an operating portion case 2, which is formed in an axially cylindrical form having an axial direction set as a longitudinal direction thereof, on the upper end side a handle portion 1 having a size large enough to be grasped by a hand and formed in an axially cylindrical form having an axial direction set as a longitudinal direction thereof, as shown in FIG. 1. Then, a motor M is internally built in the handle portion 1 of the main body, and a switch lever 10 for controlling a drive circuit of the motor M to be on and off is mounted on the front side of the handle portion. In addition, the switch lever 10 is linked with a control circuit within a control box 11 separately provided so as to variably control the rotational speed of the motor M according to the depth in gripping the handle portion, and a switch 12 is provided on the rear side of the handle portion so as to reverse the rotational direction of the motor M.
In the operating portion case 2, a screw shaft S transmitted from and rotated by the output shaft of the motor M through a worm gear G is accommodated and axially suspended at such a posture that an axial direction thereof is set along the longitudinal direction, and a driver 20 provided so as to slide back and forth within the operating portion case 2 is screwed onto the screw shaft S so that the driver 20 is moved back and forth by the rotation of the screw shaft S. The rear end of an operating rod 21 having the rear end side projected into the operating portion case 2 at such a posture that a longitudinal direction thereof is set along the longitudinal direction is integrally connected to the driver 20 so that the front end side of the operating rod 21 is operated to go in and out of the front end of the operating portion case 2 by operating the motor M. Then, a connection hardware 22 for connecting a cartridge holder 3 to the operating portion case 2 is provided on the front end of the operating portion case in such a ring form as to surround the front end side of the operating rod 21 for making the going in-and-out operation described above, and the front end of the operating portion case is connected with the base end of the cartridge holder 3 loaded with a cartridge 4, in which an injection is sealed. An injection needle 5 having a communicating needle 50 provided on the base end side so as to be projected into the sealed portion of the front end of the cartridge 4 is mounted on an injection needle connection hardware 30 provided on the tip end side of the cartridge holder 3. The injection device of the prior art is constituted so as to inject an injection by operating the switch lever 10 to operate the motor M under the condition that a plug socket 14 at the tip end of a power source cord 13 drawn to the lower end side of the handle portion 1 is plugged in the socket of a commercial power source.
The means described above enables injection of an anesthetic into a patient's gingiva at such an extremely slow speed as to give no pain to the patient by controlling the depth in gripping the switch lever 10 when the anesthetic is injected into the patient's gingiva. However, in case of exchanging the injection needle 5 and the cartridge 4 with a new injection needle 5 and a new cartridge 4 for every patient for the prevention of an infectious disease, it is necessary to return the operating rod 21 in such a projected condition thereof to push a piston 41, which is made of a rubber plug on the rear end side of the cartridge 4, into the cartridge 4 in the operation when a drug is injected into the previous patient, to the condition that the operating rod is drawn in by reversely rotating the motor M by the operation of the reverse rotation switch 12. Since the operation for the process described above is slow and it requires a long waiting time, this prior art has a disadvantage in that the prompt exchange of the injection needle with a new one is not possible.
Since the operation for drawing back the operating rod 21 by operating the switch 12 is assumed as an object for the case that the aspiration operation is carried out for confirming the condition that the needle 5 is pierced into a predetermined portion of the patient's gingiva up to a predetermined depth when the needle 5 is pierced into each patient's gingiva, the speed for the operation of the operating rod 21 is set to be extremely slow.
Since the injection of an anesthetic by pushing out the operating rod 21 is set up in an extremely slow speed to such an extent that no pain is given to each patient, the variable control of the rotational speed of the motor M by the control of the depth in gripping the switch lever 10 cannot also accelerate the drawing-back speed of the operating rod 21, even though this control circuit is used. Furthermore, even though the rotation of the motor M is switched over to a high speed rotation by use of decelerating means composed of the worm gear G for the transmission between the screw shaft S and the output shaft of the motor M, the prior art takes such an impossible mechanism as to move the operating rod at high speed.